Unexpected MV from longer barrel?

[punkwood2k]

I have MV history on several different charge weights from my 22" sporter barrel. I moved up to a 26" heavy Barrel, and tested today using the same charge ranges I had previous data on. Because of the longer barrel, I expected slightly higher MV figures.. But in reality, my MV was LOWER by about 3% across the board than the shorter barrel... any opinions WHY?

Possible explanations...

26" barrel is brand new... would that effect MV?
or
my chrono wasnt working / set up properly...
or
I need a slower powder for longer barrel? Tested with CFE223.

Thoughts?

 

[RobertB]

What kind of bbls? Has this been confirmend with actual drop? What kind of chrono.

 

[gvanhyning]

New barrel ... Check velocity after you have about 150+ shots on the barrel.


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[FCS]

I have MV history on several different charge weights from my 22" sporter barrel. I moved up to a 26" heavy Barrel, and tested today using the same charge ranges I had previous data on. Because of the longer barrel, I expected slightly higher MV figures.. But in reality, my MV was LOWER by about 3% across the board than the shorter barrel... any opinions WHY?

Possible explanations...

26" barrel is brand new... would that effect MV?
or
my chrono wasnt working / set up properly...

Thoughts?

What chamber in the 22" bbl? What chamber in 26" bbl?
Factory bbls or custom barrels?
Same brand brass used in both rifles?
Same lot # of powder used in both rifles?

When the number of unknowns exceeds the number of knows by an unknown amount...you are doomed to the wrong answer.

I think you need to better define the parameters to get a reasonable answer.

 

[punkwood2k]

What kind of bbls? Has this been confirmend with actual drop? What kind of chrono.

Baseline MV was a 22" sport / hunting profile (pencil thin Savage) 1:10 twist
New barrel is a 26" Varmint / Heavy , 1:10 twist

No, chrono reading were not verfied with drop measurments.. Its a Shooting Chrony chrono.. Possible Chrono error, since I was shooting dusk, and this thing only likes full daylight?

 

[punkwood2k]

What chamber in the 22" bbl? What chamber in 26" bbl?
Factory bbls or custom barrels?
Same brand brass used in both rifles?
Same lot # of powder used in both rifles?

When the number of unknowns exceeds the number of knows by an unknown amount...you are doomed to the wrong answer.

I think you need to better define the parameters to get a reasonable answer.

All variables are the same EXCEPT the barrel length.. Both factory barrels (but different manufacture, Savage (old) & Remington (new) in .308

 

[MontanaMarine]

The Rem has a long throat, that typically reduces pressure/velocity in direct comparison with a shorter throat. Might be the culprit.

 

[punkwood2k]

The Rem has a long throat, that typically reduces pressure/velocity in direct comparison with a shorter throat. Might be the culprit.

The Remington DOES have a 0.070" longer throat than the Savage..

 

[FCS]

All variables are the same EXCEPT the barrel length.. Both factory barrels (but different manufacture, Savage (old) & Remington (new) in .308

Variables are anything but "all variables are the same EXCEPT the barrel length".

What is OAL to touch lands in Savage barrel?
What is OAL to touch lands in Rem barrel?

 

[FCS]

The Remington DOES have a 0.070" longer throat than the Savage..

Right there is your velocity difference.

 

[bigedp51]

Besides missing the throat variations, you forgot to figure in the drag coefficient of the new button rifled barrel. (very rough humor)

Throat.

Two inches from the muzzle.

Custom made hand lapped barrel.

After fire lapping a new button rifled barrel. (Half rough humor)

The throat on my Savage .223 is longer than the throats on my AR15 5.56 rifles.

 

[M40_A1]

Temperature difference (last summer vs. this winter?)? Barrel can make a big difference, too.

 

[punkwood2k]

So, since I am working with a longer throat that prevents me from seating anywhere near the lands (magazine limited OAL), is there anything I can do to regain the lost velocity besides a higher charge weight? I moved up to the 26" barrel so I could extend the range of my .308 to 1000 yds and beyond, but now it looks like my el-cheapo 22" savage still has more range.. To make matters worse, on my OCW test I just ran, it looks like the node for the new rifle is an anemic 2670 fps with my 175gr Nosler CC. Compared to my Savage node of 2800fps with the same bullet. :-(

 

[punkwood2k]

Temperature difference (last summer vs. this winter?)? Barrel can make a big difference, too.

Temp difference isnt a factor this time.. Original numbers were recorded at 56 F, new numbers recorded at 59 F. Same altitude, same general mmHg..

 

[punkwood2k]

Besides missing the throat variations, you forgot to figure in the drag coefficient of the new button rifled barrel. (very rough humor)

Jesus, thats what a barrel looks like under a scope? UGLY!!! I've heard about Fire Lapping a barrel.. Does that actually work? I've heard very adamant opinions both ways on that..

 

[farmerbrown]

Hmmm,

Well, I've not much experience with CFE223, but it looks slower than Varget, so I wouldn't expect the powder to be an issue.

To me, there are three avenues for investigation:

1. The load and the pressure/velocity generated by the load
2. The differing friction in the barrel
3. The chony

1. Presuming you use the same brass/load/COAL in each case, this powder isn't unusually fast then I think this is an unlikely cause. Of course, the long Remington throat can be a factor. Less initial resistance could mean lower pressure and lower velocity. I presume the Savage has a standard chamber and isn't overly tight?

2. There ARE cases where the longer barrel will give lower velocity. M855 in a barrel over 20" is one case in a study I've just read. The reason is simple: if the force behind the bullet isn't greater than the friction in the increased length of barrel - you'll get less velocity. This is slightly more complicated when you have two different barrels, since early resistance to the bullet will cause the pressure to increase dramatically which can (paradoxically) increase the velocity.

3. Over the past several years, I've scratched my head several times trying to fix/understand problems that originating in readings from a Chrony. I threw mine out. You don't say how much CFE you used, but I'm thinking that 2800 is moving for a 175 out of a 22" barrel??

I'm leaning towards 3, but you've not given enough information to rule out the others.

 

[punkwood2k]

Hmmm,

3. Over the past several years, I've scratched my head several times trying to fix/understand problems that originating in readings from a Chrony. I threw mine out. You don't say how much CFE you used, but I'm thinking that 2800 is moving for a 175 out of a 22" barrel??

That 2800fps is 47.1gr CFE223, in my Savage 22". That same charge only gave me 2730fps in my R700 26".. Notable difference is that the jump in the Savage is 0.025", but the Remington jump is 0.102".. BIG difference... I'm gathering that has more of an impact on MV than I thought it would.

 

[farmerbrown]

Yeah,

Wow - that's a bunch.

I agree - playing with Quickload for a few years - it's amazing what a difference in COAL and case capacity make (although it cannot model 'throat').
If you have confidence in your Chrony (as I said, I proved mine was junk) then it would be a fair assumption as the most likely cause.

One test to try and nail it down could be to load up a few single rounds and give them a somewhat similar 'jump' to see if the velocity goes up.
Personally, I'm not sure this will help, because the increased case capacity is working against you. Others might have better ideas?

If muzzle velocity is really that important to you, the best bet might be to do what I did with my 26" Remington PSS barrel = cut a new chamber in it with a throat better suited to 175 with 2.800" COAL.
Mine now gets faster muzzle velocity than that of my colleagues with the same load although our ammo is interchangeable and the barrel isn't quite 26" any more